1. Field of the Invention
The present invention relates to a static var compensator, and more specifically to a static var compensator using a TSC (Thyristor Switched Capacitor).
2. Description of the Background Art
In order to compensate for reactive power of an electric power system, TSCs are used. Specifically, the TSCs that are series circuits each including a capacitor and a thyristor are connected in parallel to a transmission line to thereby supply leading reactive power to the system.
For example, Japanese Patent Laying-Open No. 62-244268 (hereinafter Patent Literature 1) discloses TSCs formed by delta-connecting three-phase series circuits each including a reactor, a capacitor, and a thyristor switch. Patent Literature 1 discloses a triggering method for thyristor switches forming the TSCs in order to reduce a difference of the triggering timing between the thyristor switches. Following the triggering method according to Patent Literature 1, all series-connected thyristor switches to be triggered are triggered almost simultaneously.
In the static var compensator, it is common to configure thyristor switches in the form of a thyristor valve and thereby ensure a required breakdown voltage and/or a required capacity.
In the TSCs, when the thyristor switches are turned off, the capacitors are charged to cause a large difference of the voltage between the terminals of the thyristor switches of different phases. It is accordingly required to provide an adequate insulation distance between the phases, which leads to a problem of an increase in size and cost of the thyristor valve. Patent Literature 1, however, does not give consideration at all to the voltage difference between the thyristor switches of different phases that occurs when the thyristor switches are turned off.